What Is Community-Acquired Pneumonia?

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There are several ways that you can develop pneumonia ranging from inhaling toxic substances in the workplace to unknowingly being infected by a bacteria in the hospital.

Any lung infection acquired outside of the hospital setting is considered community-acquired pneumonia (CAP).

Viruses and certain bacteria such as streptococcus pneumoniae (S. pneumoniae), haemophilus influenzae, and atypical bacteria—like chlamydia pneumoniae, mycoplasma pneumoniae, and Legionella species—are among the most common culprits of CAP.

This article discusses the symptoms, causes, treatment, and prognosis for community-acquired pneumonia.

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Symptoms

The clinical presentation of CAP varies wildly depending on the range. For example:

  • Mild pneumonia is characterized by fever and a productive cough.
  • Severe pneumonia is characterized by difficulty breathing and sepsis.

Symptoms of CAP often develop quickly and are accompanied by a racing heartbeat, sweating, and feeling warm. These are subjective signs that an infection is brewing.

The most common symptoms of CAP include:

  • Shortness of breath
  • Productive cough (coughing with green or whitish phlegm)
  • Fever and chills
  • Chest pain that is worse when you breathe or cough
  • Upper belly (abdomen) pain
  • Nausea and vomiting
  • Diarrhea

Causes

The most common culprits of CAP are viruses—namely the influenza virus and bacteria. Less commonly, fungi and parasites can trigger lung infection. 

Streptococcus pneumoniae is the most common bacterial cause of CAP, but other common germs include: 

  • Haemophilus influenzae
  • Mycoplasma pneumoniae
  • Chlamydia pneumoniae
  • Legionella
  • Gram-negative bacilli
  • Staphylococcus aureus

Viruses can also cause CAP. In fact, viral infection, like having the flu, puts you at higher risk of getting bacterial pneumonia, which is often more severe. Aside from the influenza virus, the following viruses can also cause CAP: 

Diagnosis

If your healthcare provider suspects CAP, they will likely ask you questions about your symptoms and perform a focused physical exam, listening to the heart and lungs for signs of infection.

They may also order a chest X-ray to look for signs of pulmonary infiltrates (like pus or blood in the lungs).

Based on CAP’s high prevalence, the presence of pulmonary infiltrates on imaging, and the severity of your symptoms, broad-spectrum antibiotics may be initiated.

In mild or moderate cases, your healthcare provider may also order the following to inform their diagnosis:

  • Blood cultures
  • Sputum gram stain and culture
  • Urinary antigen testing for S. pneumoniae
  • Testing for Legionella spp.
  • SARS-CoV-2 testing
  • Complete blood cell count (CBC)

Treatment 

The type of treatment that you receive largely depends on:

  • Your symptom severity
  • Presence of comorbidities
  • Location at which you are receiving treatment (inpatient or outpatient)

Viral CAP usually does not need antibiotics and resolves on its own with the help of supportive treatment.

Antibiotics are the mainstay of treatment for bacterial CAP. Amoxicillin and doxycycline are preferred in low-risk people. Five- to 10- day treatment courses are recommended for all people with CAP, with reassessment following treatment. 

For people affected with CAP who do not have comorbid conditions or risk factors for drug-resistant pathogens, monotherapy (treatment using a single drug) with amoxicillin, doxycycline, or a macrolide (azithromycin or clarithromycin) is recommended.

For people affected with CAP who have comorbidities, the guidelines recommend broader-spectrum coverage consisting of either monotherapy with a respiratory fluoroquinolone (levofloxacin, moxifloxacin, or gemifloxacin) or combination therapy with amoxicillin-clavulanate or a cephalosporin plus a macrolide or doxycycline.

Choosing the Right Antibiotic

The specific type of antibiotic that you will use will also be based on:

  • Your allergy profile
  • Past antibiotic use
  • Bacterial resistance in the area
  • Possibility of adverse effects

Any person with CAP who was recently exposed to one class of antibiotics should be treated with an antibiotic regimen involving a different class to avoid bacterial resistance. Healthcare providers will also collect data on MRSA and pseudomonas bacterial resistance to inform their choices of bacteria.

Sputum (phlegm) cultures are only recommended in severe cases. Routine blood cultures, sputum cultures, and urinary antigen testing are not beneficial in people with non-severe CAP. 

When to See a Healthcare Provider

It may be difficult to suspect CAP especially, if you are sick.

Studies show that people who get treatment early fare much better than those who do not. If you feel ill for more than a few days, are not improving with over-the-counter medications or antibiotics, or are experiencing chest pain, productive cough, or shortness of breath, seek immediate medical attention.

Prognosis

CAP is a leading cause of morbidity and mortality worldwide and the seventh leading cause of death in the United States, accounting for more than 4.5 million outpatient and emergency room visits annually. In fact, CAP is the second most common cause of hospitalization and the most common infectious cause of death in the United States. 

The following risk factors, when present, increase your risk of morbidity and mortality:

  • Older age
  • The presence of pre-existing health conditions
  • Smoking and alcohol overuse
  • Living in crowded conditions, such as nursing homes and mass incarceration sites
  • Having a medical condition that can impact the airway (such as stroke, seizure, anesthesia, drug or alcohol use, esophageal lesions, or dysmotility)
  • Weakened immune system, such as from drug treatment or a health problem like diabetes, cancer, or HIV

CAP has a highly variable outlook ranging from rapid recovery to life-threatening complications. The mortality associated with CAP greatly depends on the clinical setting where it is treated, ranging from 3% to 30% in most studies, and when therapy is initiated. Generally, the sooner antibiotics or antivirals are initiated, the better the prognosis.

Efforts to improve the outlook for those with CAP are mainly geared toward helping populations at the highest risk of mortality. Severe CAP is associated with significant mortality, and despite effective antibiotic therapy, between 16% to 36% of people affected with CAP may die within a short period of time.

Summary

Any lung infection acquired outside of the hospital setting is considered community-acquired pneumonia (CAP). The influenza virus and streptococcus pneumoniae are the most common viral and bacterial culprits, respectively. 

A Word From Verywell

CAP is a significant contributor to mortality, especially in the sick and older adults. If you are at high risk of CAP, knowing the signs and symptoms to look out for is important to get the help that you need. 

Most cases of CAP are caused by viruses and don't require treatment with antibiotics. Completing your vaccine regimen as directed by a healthcare provider lowers your risk of CAP. Bacteria are less likely to cause CAP, but when they do the cases tend to be more severe. If bacteria is the cause of your CAP, antibiotics are the mainstay treatment, and it is imperative that you take your medication exactly as prescribed by your healthcare provider.

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6 Sources
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